The modernization of elevators in prior art generally focuses on elevators that no longer technically and/or otherwise meet the requirements of the time. Modernization might focus on some subfunctions or subsystems, or at its most extreme might mean the complete renewal or essentially complete renewal of elevators. Points to be possibly modernized include, inter alia: the control system of the elevator; the hoisting function, with machinery and roping, of the elevator; the doors of the elevator; and the elevator car. Maintenance procedures of elevators, on the other hand, maintain the existing systems and functionality of an elevator. Thus it is normal that when the hoisting ropes have worn out, they are replaced with new ones and, generally in this case, with similar ones. At the same time the traction sheave can be renewed or overhauled. Thus, for example, also the replacement ropes will last for essentially the same time as the old ropes had lasted. Correspondingly, when renewing a traction sheave, the new traction sheave corresponds in its properties to the previous traction sheave. Maintenance activities do not, nor generally do modernizations either, result in substantial changes to the roping arrangement.
When addressing the lifetime of hoisting ropes, it is good to know that in traction sheave elevators the rope tension of an elevator rope passing over the traction sheave on different sides of the traction sheave is usually of a different magnitude, which endeavors inter alia to cause slipping of the hoisting rope in the rope groove of the traction sheave. The tension differences result from the counterweight on the one side of the traction sheave not being of the same weight as the elevator car with load on the opposite side of the traction sheave. Sometimes the elevator car is empty, sometimes full and sometimes between these. On the other hand, the mass of the counterweight does not generally change. The aim is to select the mass of the counterweight to be as optimal as possible bearing in mind different loads of the elevator car, but this is not necessarily sufficient in all situations. These types of situations can be e.g. accelerations, brakings and emergency stops. Up to a certain limit the slipping of ropes on a traction sheave resulting from a tension difference is easy to control, but often the friction of metallic rope grooves is not sufficient for managing sudden large tension differences, in which case the elevator ropes start to slip too much in the rope grooves of the traction sheave.
According to prior art, the aim has been to improve the friction needed in the rope grooves of the traction sheave by, among other things, making an undercut that is wider than usual in the rope grooves. This solution does indeed increase the friction but at the same time the stressing of the elevator rope increases, because the support surface of the elevator rope in the rope groove decreases. In practice this solution is not for this reason advantageous, because the lifetime of ropes decreases as the stressing of the ropes increases.
One way of improving friction is presented in the solution according to Japanese patent publication no. JP54124136 (A). In it, a material that improves friction, such as asbestos, is disposed in the undercut of the rope grooves, which material presses from below against the elevator rope, pushed by a separate flexible material that is lower in the same undercut. As the asbestos wears, the flexible material pushes the asbestos ring towards the elevator rope. A problem in this solution is inter alia that a two-component material in an undercut groove is difficult to control. The elevator rope endeavors to push the asbestos ring in front of it under the effect of friction, in which case a force acts on the interface between the asbestos and the flexible material, which force might break the structure. In addition, this type of structure is extremely difficult to dimension correctly.
Correspondingly, United States patent publication no. U.S. Pat. No. 1,944,426 presents in FIG. 1 a rope sheave solution, in which the base of a metallic rope groove of a metallic rope sheave comprises a groove which is filled with rubber, which is glued to the groove. The purpose of the rubber here is, however, to save the steel rope from wear by letting the steel rope expand in the direction of the rubber. There is no mention in the publication about the improvement of frictive traction, nor does it become clear from the publication how the rope groove, the height of the rubber and the diameter of the steel rope are mutually dimensioned.
According to prior art, frictive traction is also improved by enlarging the angle of contact between the elevator ropes and the traction sheave. In this case e.g. so-called double-wrap (DW) and extended single-wrap (ESW) structures are used, in which an angle of contact of approx. 270-360 degrees can easily be obtained, and also over 360 degrees can be obtained when the ropes are passed around the traction sheave by more than one rotation. The result is good frictive traction, but one problem in these solutions is rope bendings that stress the ropes, which bendings wear the ropes and thus shorten the lifetime of the ropes.